1. Field of the Invention
The present invention relates to a method of determining exposure conditions, an exposure method, a device manufacturing method, and a storage medium, and more specifically to a method of determining exposure conditions in transferring a pattern formed on a mask onto a substrate, an exposure method that exposes under the exposure conditions determined by the determining method, a device manufacturing method that uses the exposure method, and a storage medium that stores the program of determining exposure conditions.
2. Description of the Related Art
To date, in a lithography process for manufacturing semiconductor devices, liquid crystal display devices, or the like, exposure apparatuses have been used which transfer a pattern formed on a mask or reticle (generically referred to as a xe2x80x9creticlexe2x80x9d hereinafter) onto a substrate such as a wafer or glass plate (hereinafter, referred to as a xe2x80x9cwaferxe2x80x9d as needed) coated with a resist, through a projection optical system. As such exposure apparatuses, a reducing projection exposure apparatus of a step-and-repeat type (so-called stepper) and a successive-movement-type exposure apparatus such as a scanning exposure apparatus of a step-and-scan type, that is an improvement on the stepper, are used mainly from the point of view of throughput.
In exposure by such an exposure apparatus, it is known that depending on the energy amount (exposure dose amount) of exposure light irradiating an exposure area on a wafer and the positional relationship between the image plane for a reticle pattern to be transferred onto and the exposure area on the wafer during exposure, that is, a focus error for the exposure area on the wafer, the shapes of the pattern""s features transferred onto the wafer vary. If the exposure dose amount is less than a desired one, the exposure of the exposure area on the wafer is not sufficient, and if the exposure dose amount is too much, the neighborhood of the exposure area is also exposed. Further, when the position of the exposure area on the wafer in the direction parallel to the projection optical system""s optical axis is not within the depth of focus of the projection optical system""s image plane for the reticle pattern, that is, when a focus error exists, an image of the reticle pattern formed in the exposure area on the wafer is blurred, so that an accurate, reduced image of the pattern cannot be formed on the wafer. Therefore, in order to project an accurate, reduced image of the pattern onto a wafer, the exposure dose amount and the position of the wafer in the optical axis direction (hereinafter, called xe2x80x9cfocus positionxe2x80x9d as needed) need be optimized.
Moreover, as semiconductor devices (integrated circuits), etc., become more highly integrated year by year, higher resolution, that is, the capability of accurately transferring more detailed dimension features is demanded of projection exposure apparatuses, which are an apparatus for manufacturing semiconductor devices, etc. In order to improve the resolution of a projection exposure apparatus, the projection optical system thereof need be improved in imaging performance, and hence, it is important to accurately measure and evaluate the imaging characteristics of the projection optical system.
In order to accurately measure an imaging characteristic, e.g. the image surface (best imaging surface), of the projection optical system, the best focus position at each measurement point must be accurately measured.
As the method of detecting the above-mentioned optimum exposure conditions and the best focus position simultaneously, a method is known which transfers a predetermined reticle pattern (for example a line-and-space pattern, etc.) as a test pattern onto a test wafer a number of times each time with a different exposure dose amount and with the wafer being at a different focus position, and which views resist images (transferred images of the pattern) obtained through the development of the test wafer by means of a scanning electron microscope (SEM) and determines the forming states thereof. That is, the exposure dose amount and the wafer""s position in the projection optical system""s optical axis direction under which a resist image has been formed whose forming state is determined to be best by the viewing are determined to be the best exposure dose amount and the best focus position respectively. Alternatively, viewing to check for each field whether or not a transferred pattern exists, the middle point of the exposure dose amount range and the middle point of the wafer""s focus position range for which a transferred pattern is determined to exist are determined to be the best exposure dose amount and the best focus position respectively.
In the above prior art method of determining exposure conditions, however, because of viewing to check results of the test exposure, if values of each of the conditions for the test exposure vary coarsely, it is easy to find a pattern in the best forming state in the test exposure wafer or check whether or not a transferred pattern exists in a field, but it is difficult to accurately obtain the best exposure conditions. Meanwhile, if values of each of the conditions for the test exposure vary finely, the time for the exposures of all fields increases, and the number of candidates for a pattern formed in the best exposure conditions is expected to increase, or it is difficult to determine the boundary between fields where a transferred pattern exists and fields where a transferred pattern does not. Hence, it is difficult to determine the best exposure conditions accurately.
Under such circumstances, an invention for solving such difficulty of the above-mentioned method of determining exposure conditions by viewing is disclosed in, for example, Japanese Patent Laid-Open No. 11-233434, where after development of a wafer on which a pattern has been transferred in test exposure, the images of the pattern""s resist images developed are picked up, and where pattern matching with a given template is performed on the image data to determine the best exposure conditions based on results of the pattern matching.
Since the invention was made, patterns have become finer in dimension, and when such a pattern is used as the test pattern, depending on the type of template pattern, performing simply pattern matching may take a long time for determining the exposure conditions to increase greatly, and it may be difficult to determine the real, best exposure conditions. Further, while correlation coefficients obtained by the pattern matching are usually compared with a given threshold value, it needs a skill to set the threshold value to an appropriate value. There is much room for improvement therein.
This invention was made under such circumstances, and a first purpose of the present invention is to provide a method of determining exposure conditions, which method can accurately obtain the best exposure conditions.
Further, a second purpose of the present invention is to provide an exposure method that can exactly perform very accurate exposure under the best exposure conditions.
Yet further, a third purpose of the present invention is to provide a device manufacturing method that can manufacture highly integrated devices with good productivity.
Still further, a fourth purpose of the present invention is to provide a program that automates the process in an exposure apparatus of determining exposure conditions and a storage medium that stores the program.
According to a first aspect of the present invention, there is provided a first exposure condition determining method with which to determine exposure conditions for transferring a pattern arranged on a first plane onto an object arranged on a second plane via a projection optical system, the method comprising the steps of transferring a test exposure pattern including a predetermined measurement pattern and a reference pattern sequentially onto a plurality of part areas on the object via the projection optical system while changing at least one of exposure conditions under consideration, the reference pattern being formed on the object having a photosensitive layer on its surface to be thicker in line width than the measurement pattern; picking up an image of the plurality of part areas on the object on each of which the test exposure pattern has been transferred under the exposure conditions of different values and performing pattern-matching with template pattern data on the image datum of each part area, the template pattern data including image data corresponding to the reference pattern; and determining the at least one exposure condition under consideration based on results of the pattern-matching for the part areas.
Herein, the term xe2x80x9cexposure conditionsxe2x80x9d refers not only to exposure conditions in the narrow sense such as illumination conditions (including the type of mask) and an exposure dose amount on the image plane, but also to exposure conditions in the broad sense including settings for all components related to exposure such as imaging characteristics of the projection optical system.
According to this, a first step transfers a test exposure pattern including a predetermined measurement pattern and a reference pattern sequentially onto a plurality of part areas on the object via the projection optical system while changing at least one of exposure conditions under consideration, the reference pattern being formed on the object having a photosensitive layer on its surface to be thicker in line width than the measurement pattern, the reference pattern being formed on the object having a photosensitive layer on its surface to be thicker in line width than the measurement pattern. As a result, the test exposure pattern including the predetermined measurement pattern and the reference pattern has been transferred on each of the plurality of part areas on the object by a test exposure under the at least one exposure condition of a different value.
A second step picks up an image of the plurality of part areas on the object on each of which the test exposure pattern has been transferred under the exposure conditions of different values and performing pattern-matching with template pattern data on the image datum of each part area, the template pattern data including image data corresponding to the reference pattern. In this case, because a feature whose image is formed on an object having a photosensitive layer on its surface to be thicker in line width than the measurement pattern""s is used as the reference pattern, it does not disappear for example even when the exposure energy amount is so large that the measurement pattern""s image disappears (overdose). Here, the phrase xe2x80x9creference pattern being formed on the object having a photosensitive layer on its surface to be thicker in line width than the measurement patternxe2x80x9d includes the case where, when the reference pattern is formed on a mask, the line width of the reference pattern is physically thicker than that of the measurement pattern on the mask, so that its transferred image is thicker in line width than the measurement pattern""s on an object, and the case where, in determining exposure conditions, the reference pattern""s transferred image is formed, while the measurement pattern""s transferred image is not formed, in the photosensitive layer on the object""s surface at an exposure energy amount in the range in which it is variable. That is, the phrase xe2x80x9cto be thicker in line widthxe2x80x9d includes one existing with the other not existing as well as literally being thicker. Therefore, the reference pattern is not limited to a line-like mask feature with a line width, but is any feature in shape whose transferred image is formed in the photosensitive layer and can be used as a reference. Hence, the reference pattern may be constituted by boundary lines between measurement patterns on a mask.
Further, because the positional relationship between the reference pattern and the measurement pattern is known, by comparing data of the reference pattern""s transferred image in each image data and image data corresponding to the reference pattern in the template pattern data, image data of the transferred image formed in each of the part areas on the object can be matched with the template pattern data, and thereby the degree of matching (correlation between the two) is obtained for each part area and the time required for template matching is shortened. In this case, by using not a subjective method such as viewing but pattern matching that is an objective, quantitative method, the state of the pattern""s transferred image for each part area is obtained.
And a third step determines the at least one exposure condition under consideration based on results of the pattern-matching for the part areas.
Therefore, according to the first exposure condition determining method, the exposure condition under consideration can be obtained stably, accurately, and quickly without making the test exposure conditions vary too finely.
In this case, in the transferring step the transfer may be performed while changing two exposure conditions under consideration; in the picking-up step, a respective correlation value between the template pattern data and the image datum of each the part area may be obtained as a result of the pattern-matching, and in the determining step, at least one of the exposure conditions under consideration may be determined based on a curve shape identified based on results of comparing the correlation values and a preset threshold value as a reference for identifying the curve shape on a two-dimensional coordinate system whose axes represent the two exposure conditions respectively. In this case, a respective correlation value (denoting the degree of matching) between the template pattern data and the image datum of each the part area is obtained by the pattern-matching, and a curve shape is identified based on results of comparing the correlation values and a preset threshold value as a reference for identifying the curve shape on a two-dimensional coordinate system whose axes represent the two exposure conditions respectively, which curve represents a boundary between correlation values above the threshold value and ones not above it in the distribution of the correlation values for the part areas, and at least one of the exposure conditions under consideration is determined based on the curve shape identified. Therefore, the exposure condition under consideration can be determined stably, accurately, and quickly.
In this case, the curve shape may be an approximate curve. In this case, a respective correlation value between the template pattern data and the image datum of each the part area is obtained by the pattern-matching, and a plurality of boundary points are obtained based on results of comparing the correlation values and a preset threshold value as a reference for calculating an approximate curve on a two-dimensional coordinate system whose axes represent the two exposure conditions respectively, and the approximate curve fitted close to the boundary points is calculated. And from a peak (or bottom) point, inflection point, or intersections with a given slice level of the calculated approximate curve, at least one of the exposure conditions under consideration can be determined.
In the first exposure condition determining method of this invention, when at least one of the exposure conditions under consideration is determined from the curve shape on the two-dimensional coordinate system, the plurality of part areas on the object may be arranged in a matrix on the object so as to form a rectangular area as a whole; the curve shape may be a shape including a mountain-like curve appearing in the rectangular area, and when picking up an image of the plurality of part areas, an image of part of the rectangular area may be picked up, in which part a mountain-like curve is, from experience, expected to exist.
In this case, an image of each of a plurality of divided areas that the target area whose image to be picked up may be divided into is picked up.
In the first exposure condition determining method of this invention, various data can be used as the template pattern data, such as pattern data calculated based on the test exposure pattern and the projection magnification of the projection optical system, or the template pattern data may be image data of at least one part area where an image of the measurement pattern does not substantially exist and which is selected from image data of the plurality of part areas on the object on which the test exposure pattern has been transferred in the transferring step. In this case, since image data of at least one part area where an image of the measurement pattern does not substantially exist (hereinafter called white pattern data, as needed) is selected as the template pattern data from image data of the part areas, the accuracy in detecting the boundary of whether the measurement pattern""s transferred image exists and its neighborhood is high. Further, since the threshold value can be set high, false recognition hardly occurs, and it can achieve ideal detection of the pattern.
In the first exposure condition determining method of this invention, the template pattern data may be image data of at least one part area having a high possibility that a transferred, best-resolved image of the measurement pattern exists (hereinafter called black pattern data, as needed) and selected from image data of the plurality of part areas on the object on which the test exposure pattern has been transferred in the transferring step.
In this case, the first method may further comprise the step of performing before the determining step pattern-matching on the image datum of each part area with using as template pattern data image data of at least one part area where an image of the measurement pattern does not substantially exist and which is selected from image data of the plurality of part areas on the object on which the test exposure pattern has been transferred in the transferring step. In this case, pattern-matching the image datum of each part area with the white pattern data as the template pattern data accurately detects the boundary of whether the measurement pattern""s transferred image exists. And based on the boundary line as the result, part areas having a high possibility that a transferred, best-resolved image of the measurement pattern exists are certainly detected, and image data (black pattern data) of any one of the part areas is used as the template pattern data, so that template pattern data meeting given requirements can be certainly selected.
In the first exposure condition determining method of this invention, when the photosensitive layer is made of a photo-resist, various features can be used as the reference pattern. For example, the reference pattern may have such a thickness that the resist image formed on the object through the development does not disappear. That is, the reference pattern""s thickness is such that its resist image on the object does not disappear through development, taking into account the characteristics of the resist and exposure conditions.
In the first exposure condition determining method of this invention, the reference pattern may be such that the orientation of a transferred image of the measurement pattern can be detected from. In this case, even when transferred images on the object are rotated relative to a reference state, e.g. an initial state, image data of each transferred image can be quickly matched with template pattern data.
In this case, the reference pattern may be a frame-like pattern arranged around the measurement pattern and which is thick in line width.
In the first exposure condition determining method of this invention, the reference pattern may be such that the magnifying/reducing ratio, as well as the orientation, of a transferred image of the measurement pattern can be detected from its transferred image""s data.
According to a second aspect of the present invention, there is provided a second exposure condition determining method with which to determine exposure conditions for transferring a pattern arranged on a first plane onto an object arranged on a second plane via a projection optical system, the method comprising the steps of transferring a measurement pattern sequentially onto a plurality of part areas on an object having a photosensitive layer on the surface thereof via the projection optical system while changing two exposure conditions under consideration; picking up an image of the plurality of part areas on the object on each of which the measurement pattern has been transferred under the exposure conditions of different values and selecting as a template pattern datum image data of at least one part area where an image of the measurement pattern does not substantially exist from the picked-up image data of the plurality of part areas; pattern-matching the image datum of each the part area with at least the selected template pattern datum to obtain a respective correlation value, and comparing the correlation values and a preset threshold value as a reference for calculating an approximate curve on a two-dimensional coordinate system whose axes represent the two exposure conditions under consideration respectively; and determining at least one of the exposure conditions under consideration based on an approximate curve calculated based on results of the comparing.
According to this, a first step transfers a measurement pattern sequentially onto a plurality of part areas on an object having a photosensitive layer on the surface thereof via the projection optical system while changing two exposure conditions under consideration. As a result, the measurement pattern""s transferred image has been formed on each of the plurality of part areas on the object by a test exposure under the at least one exposure condition of a different value.
Next, a second step selects as a template pattern datum image data of at least one part area where an image of the measurement pattern does not substantially exist from picked-up image data of the plurality of part areas on the object on each of which the measurement pattern has been transferred under the exposure conditions of different values by the test exposure.
Next, a third step pattern-matches the image datum of each the part area with at least the selected template pattern datum to obtain a respective correlation value, and compares the correlation values and a preset threshold value as a reference for calculating an approximate curve on a two-dimensional coordinate system whose axes represent the two exposure conditions under consideration respectively, and calculates the approximate curve fitted close to a plurality of boundary points obtained based on the comparing results. Here, since white pattern data is selected as the template pattern data, the accuracy in detecting the boundary of whether the measurement pattern""s transferred image exists and its neighborhood is high. Further, since the threshold value can be set high, false recognition hardly occurs, and it can achieve ideal detection of the pattern.
And a fourth step, from a peak (or bottom) point, inflection point, or intersections with a given slice level of the calculated approximate curve, determines at least one of the exposure conditions under consideration.
Therefore, the second exposure condition determining method of this invention can determine exposure conditions under consideration stably and accurately.
In this case, the threshold value may be determined based on a distribution of correlation values obtained beforehand by pattern-matching.
In this case, the distribution of correlation values may be a distribution obtained by normalizing correlation values of the part areas obtained by the pattern-matching.
When the template pattern data is white pattern data, it is difficult to determine an appropriate value as the threshold value, but according to this method, the threshold value can be determined easily and appropriately.
In the second exposure condition determining method of this invention, in the selecting step, image data of at least two part areas satisfying the condition each may be selected as the template datum, and when, in performing the pattern-matching step with using one of the selected template data, an approximate curve cannot be calculated, the pattern-matching step may be performed again using at least one of the rest of the selected template data.
According to a third aspect of the present invention, there is provided a third exposure condition determining method with which to determine exposure conditions for transferring a pattern arranged on a first plane onto an object arranged on a second plane via a projection optical system, the method comprising the steps of transferring a measurement pattern sequentially onto a plurality of part areas on an object having a photosensitive layer on the surface thereof via the projection optical system while changing two exposure conditions under consideration; picking up an image of the plurality of part areas on the object on each of which the measurement pattern has been transferred under the exposure conditions of different values and selecting as first template pattern data image data of at least one part area having a high possibility that a transferred, best-resolved image of the measurement pattern exists from the picked-up image data of the plurality of part areas; pattern-matching the image datum of each the part area with the selected first template pattern data to obtain a respective correlation value, and comparing the correlation values and a preset threshold value as a reference for calculating a curve shape on a two-dimensional coordinate system whose axes represent the two exposure conditions under consideration respectively; and determining at least one of the exposure conditions under consideration based on the curve shape calculated.
A first step transfers a measurement pattern sequentially onto a plurality of part areas on an object having a photosensitive layer on the surface thereof via the projection optical system while changing two exposure conditions under consideration. As a result, the measurement pattern has been transferred on each of the plurality of part areas on the object by a test exposure under the at least one exposure condition of a different value.
Next, a second step selects as first template pattern data image data of at least one part area having a high possibility that a transferred, best-resolved image of the measurement pattern exists from picked-up image data of the plurality of part areas on the object on each of which the measurement pattern has been transferred under the exposure conditions of different values by the test exposure.
Next, a third step pattern-matches the image datum of each the part area with the selected first template pattern data (black pattern data) to obtain a respective correlation value, and comparing the correlation values and a preset threshold value as a reference for calculating a curve shape on a two-dimensional coordinate system whose axes represent the two exposure conditions under consideration respectively, and calculates the curve shape based on the comparing results.
And a fourth step determines at least one of the exposure conditions under consideration based on the curve shape calculated.
Therefore, the third exposure condition determining method of this invention can determine exposure conditions under consideration stably and accurately without using viewing, which is subjective.
In this case, when the plurality of part areas on the object are arranged in a matrix on the object so as to form a rectangular area as a whole, the curve shape may be a shape including a mountain-like curve appearing in the rectangular area, and when picking up an image of the plurality of part areas, an image of part of the rectangular area may be picked up, in which part a mountain-like curve is, from experience, expected to exist.
In this case, an image of each of a plurality of divided areas that the target area whose image to be picked up is divided into may be picked up.
The third exposure condition determining method of this invention may further comprise the steps of selecting, before the selecting step, as second template pattern data image data of at least one part area where an image of the measurement pattern does not substantially exist from image data of the plurality of part areas; and pattern-matching the image datum of each the part area with at least the selected second template pattern data to obtain a respective correlation value, and comparing the correlation values and a preset threshold value as a reference for calculating a curve shape on a two-dimensional coordinate system whose axes represent the two exposure conditions under consideration respectively, the third method wherein in the step of selecting as first template pattern data, image data of at least one part area where a transferred, best-resolved image of the measurement pattern is, based on the curve shape obtained in the pattern-matching step, expected to exist is selected as the first template pattern data.
In this case, pattern-matching the image datum of each part area with the white pattern data as the second template pattern data accurately detects the boundary of whether the measurement pattern""s transferred image exists. And based on the boundary line as the result, part areas having a high possibility that a transferred, best-resolved image of the measurement pattern exists are certainly detected, and image data of any one of the part areas is used as the first template pattern data, so that the first template pattern data meeting given requirements can be certainly selected.
In this case, when the plurality of part areas on the object are arranged in a matrix on the object so as to form a rectangular area as a whole, the selecting of the second template pattern data may be based on results of judging for part areas whether or not a transferred image of the measurement pattern exists in each of the part areas by obtaining the average of data in a predetermined detection window at each movement position, while sequentially moving the detection window in at least part of the rectangular area.
In the third exposure condition determining method of this invention, in the pattern-matching step, comparing the correlation values with a different one of a plurality of threshold values may be repeated, and the curve shape may be calculating for the different threshold value, and in the determining step, at least one of the exposure conditions under consideration may be determined based on at least two of the curve shapes each calculated for the respective threshold value.
In any one of the first through third exposure condition determining methods of this invention, a target for the picking-up may be a latent image formed in the photosensitive layer, or when the photosensitive layer is made of a photo-resist, a target for the picking-up may be a resist image obtained by developing the object. Here, the photosensitive layer is not limited to a photo-resist, but can be an optical record layer, photo-magnetic record layer, or the like, and an object having the photosensitive layer formed thereon is not limited to a wafer or a glass plate, but can be a substrate on which an optical record layer or photo-magnetic record layer can be formed.
In any one of the first through third exposure condition determining methods of this invention, various items are considered as the exposure conditions, and the exposure conditions under consideration may include at least one of position of the object in the optical axis direction of the projection optical system and the energy amount of an energy beam irradiating the object. In this case, at least one of the best focus position and the best exposure dose amount on the image plane can be determined stably and accurately without using viewing, which is subjective.
In any one of the first through third exposure condition determining methods of this invention, various patterns can be used as the measurement pattern. For example, the measurement pattern may include either of a line-and-space pattern having a duty ratio of 1/n, where n is not equal to zero, and a periodic pattern of contact holes, or may include either of an isolated line and an isolated contact hole. In the former case, a duty ratio with which the periodic pattern is viewed as isolated features is less than 1/3 for example.
In any one of the first through third exposure condition determining methods of this invention, when picking up an image of a plurality of part areas on the object, an image of part of the rectangular area may be picked up, in which part a peak point of the mountain-like curve or approximate curve is, from experience, expected to exist, but not being limited to this, image data of some part areas out of image data of the plurality of part areas may be used, or for some part areas such a correlation value may be calculated. In any case, the processing time can be shortened.
According to a fourth aspect of the present invention, there is provided a fourth exposure condition determining method with which to determine exposure conditions for transferring a pattern arranged on a first plane onto an object arranged on a second plane via a projection optical system, the method comprising the steps of transferring a measurement pattern sequentially onto a plurality of part areas on an object having a photosensitive layer on the surface thereof via the projection optical system while changing at least one of exposure conditions under consideration; acquiring a piece of information about the formation state of the pattern in each of the plurality of part areas on the object on each of which the measurement pattern has been transferred under the exposure conditions of different values; and comparing repeatedly the pieces of information about the formation states of the patterns in the part areas obtained in the acquiring step with a different one of a plurality of preset threshold values as references for calculating the one of the exposure conditions, and detecting a range of the threshold values in which values of the one of the exposure conditions under consideration calculated based on respective threshold values vary within a predetermined range and which range is continuous and not shorter than a predetermined length, and determining a best exposure condition based on the values for the threshold value range of the one of the exposure conditions under consideration.
According to this, a first step transfers a measurement pattern sequentially onto a plurality of part areas on an object having a photosensitive layer on the surface thereof via the projection optical system while changing at least one of exposure conditions under consideration. As a result, the measurement pattern has been transferred on each of the plurality of part areas on the object by a test exposure under the at least one exposure condition of a different value.
Next, a second step acquires a piece of information about the formation state of the pattern in each of the plurality of part areas on the object on each of which the measurement pattern has been transferred under the exposure conditions of different values. Here, the type of information about the formation state of a pattern depends on the method of detecting the part areas. That is, when picking up an image of a part area by light, the information is image data or data obtained by processing the image data, and when scanning a laser beam across the part area and detecting reflected or scattered beams, it is light-intensity signals or signals obtained by processing the light-intensity signals, and when illuminating the part area with laser beams slightly different in frequency and detecting the interference of diffracted beams from the part area (a so-called heterodyne detection method), it is position information or information obtained by processing the position information. Other detection methods produce respective types of information.
And a third step detects, when having repeated comparing the pieces of information about the formation states of the patterns in the part areas obtained in the acquiring step with a different one of a plurality of preset threshold values as references for calculating the one of the exposure conditions, a range of the threshold values in which values of the one of the exposure conditions under consideration calculated based on respective threshold values vary within a predetermined range and which range is continuous and not shorter than a predetermined length, and determines a best exposure condition based on the values of the one of the exposure conditions under consideration for the range. That is, after having repeated comparing the pieces of information about the formation states of the patterns in the part areas with a different one of the plurality of preset threshold values, detecting a range of the threshold values in which values of the one of the exposure conditions under consideration vary within a predetermined range and which range is continuous and not shorter than a predetermined length determines a best exposure condition easily and certainly, thereby solving the difficulty in determining a threshold value.
In this case, in the acquiring step, an image datum as a result of picking up each of the plurality of part areas on the object may be pattern-matched with a predetermined template pattern data to obtain a respective correlation value, and in the detecting step, comparing the correlation values and a different one of the threshold values may be repeated.
In this case, a target for the picking-up may be a latent image formed in the photosensitive layer, or when the photosensitive layer is made of a photo-resist, a target for the picking-up may be a resist image obtained by developing the object. Here, the photosensitive layer is not limited to a photo-resist, but can be an optical record layer, photo-magnetic record layer, or the like, and an object having the photosensitive layer formed thereon is not limited to a wafer or a glass plate, but can be a substrate on which an optical record layer or photo-magnetic record layer can be formed.
In the fourth exposure condition determining method of this invention, there are various techniques as the technique of determining a best exposure condition in the detecting step such as determining it as the value of the exposure condition corresponding to the middle of the detected range of threshold values. For example, in the detecting step, one of the average and weighted average of values of the one of the exposure conditions under consideration over the detected range may be determined to be a best exposure condition.
According to a fifth aspect of the present invention, there is provided an exposure method with which to transfer a pattern formed on a mask onto a substrate via a projection optical system by an exposure energy beam irradiating the mask, the exposure method comprising the steps of setting exposure conditions for exposure, taking into account exposure conditions under consideration determined according to any one of the first through fourth exposure condition determining methods of this invention; and transferring the pattern formed on the mask onto the substrate via the projection optical system under the set exposure conditions.
According to this, exposure conditions for exposure are set taking into account exposure conditions under consideration determined according to any one of the first through fourth exposure condition determining methods of this invention, and a pattern formed on a mask is transferred onto a substrate via the projection optical system by illuminating the mask with an exposure energy beam under the set exposure conditions, and thereby the fine dimension pattern can be accurately transferred onto the substrate.
Moreover, by using the exposure method of this invention in a lithography process, patterns can be accurately formed on a substrate, so that highly integrated micro-devices can be manufactured with high productivity and high yield. Therefore, according to another aspect of the present invention, there is provided a device manufacturing method using the exposure method of this invention.
Furthermore, any exposure condition determining method of this invention is performed by making the control computer of an exposure apparatus execute the procedures of transferring a measurement pattern sequentially onto a plurality of part areas on an object having a photosensitive layer on its surface via the projection optical system while changing at least one of exposure conditions under consideration; picking up an image of the respective images transferred on the plurality of part areas on the object each under the exposure condition of different values and performing pattern-matching with predetermined template pattern data on the respective image data of the part areas; and determining the at least one exposure condition under consideration based on results of the pattern-matching, thereby automating the determination of exposure conditions for the exposure apparatus. Therefore, according to still another aspect of the present invention, there is provided a program making a computer execute the procedures and a storage medium which stores the program and can be read by a computer.
It is noted that in automating the determination of exposure conditions, the alignment detecting system of an image processing type of the exposure apparatus can be used as an image pickup unit.